SUMMARY - 1 SUMMARY Valuable information on translation...

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1 SUMMARY Valuable information on translation initiation is available from biochemical data and recently solved structures. We present a detailed description of current knowledge about the structure, function, and interactions of the individual components involved in bacterial translation initiation. The first section describes the ribosomal features relevant to the initiation process. Subsequent sections describe the structure, function, and interactions of the mRNA, the initiator tRNA, and the initiation factorsIF1, IF2, and IF3. Finally, we provide an overview of mechanisms of regulation of the translation initiation event. Translation occurs on ribonucleoprotein complexes called ribosomes. The ribosome is composed of a large subunit and a small subunit that hold the activities of peptidyltransfer and decode the triplet code of the mRNA, respectively. Translation initiation is promoted by IF1, IF2, and IF3, which mediate base pairing of the initiator tRNA anticodon to the mRNA initiation codon located in the ribosomal P-site. The mechanism of translation initiation differs for canonical and leaderless mRNAs, since the latter is dependent on the relative level of the initiation factors. Regulation of translation occurs primarily in the initiation phase. Secondary structures at the mRNA ribosomal binding site (RBS) inhibit translation initiation. The accessibility of the RBS is regulated by temperature and binding of small metabolites, proteins, or antisense RNAs. The future challenge is to obtain atomic-resolution structures of complete initiation complexes in order to understand the mechanism of translation initiation in molecular detail. INTRODUCTION Protein biosynthesis occurs on large macromolecular ribonucleoprotein complexes named ribosomes in a process termed translation. The ribosomes are enzymatic complexes that catalyze peptide bond formation and synthesize polypeptides based on the genetic code of the mRNA. Translation is conceptually divided into four phases: initiation, elongation, termination, and ribosome recycling. The ribosome is composed of a large and a small subunit, which are assembled on the translation initiation region (TIR) of the mRNA during the initiation phase of translation. In the following elongation phase, the mRNA is decoded as it slides through the ribosome and a polypeptide chain is synthesized. Elongation continues until the ribosome encounters a stop codon on the mRNA and the process enters the termination phase of protein synthesis. Newly synthesized protein is released from the ribosome. In the final ribosome recycling phase, the ribosomal subunits dissociate and the mRNA is released. Each phase is regulated by a number of different factors. Reviews of the phases are available ( 52 , 208 ). Although the main events of the translation process are universally
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This note was uploaded on 04/22/2011 for the course BIOCHEM 412 taught by Professor Thomas during the Spring '11 term at Tennessee Martin.

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SUMMARY - 1 SUMMARY Valuable information on translation...

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